A fuel cell converts chemical energy directly into electric energy by supplying a fuel and an oxidant to two electrically-connected electrodes each and electrochemically oxidizing the fuel. Unlike thermal power generation, a fuel cell is not limited by the Carnot cycle; therefore, it shows high energy conversion efficiency. A fuel cell is generally constituted of a stack of single cells, each of which has a membrane electrode assembly as the basic structure, in which an electrolyte membrane is sandwiched between a pair of electrodes.
Supported platinum and platinum alloy materials have been used as the catalyst of the anode and cathode electrodes of a fuel cell. However, platinum in an amount that is required of today's electrode catalyst, is still expensive to realize commercial mass production of fuel cells. Accordingly, studies to reduce the amount of platinum contained in the cathode and anode of a fuel cell by combining platinum with a less expensive metal, have been carried out.
In recent years, as a catalyst for electrodes of fuel cells, core-shell fine catalyst particles have attracted attention. From the viewpoint of increasing the coverage of a core with a shell, generally in the area of methods for producing core-shell fine catalyst particles, such a method that a monatomic layer is formed in advance on a core surface by an under potential deposition method such as Cu under potential deposition method (hereinafter may be referred to as Cu-UPD) and then the monatomic layer is substituted with a shell, is known.
As a technique using the Cu-UPD method, a method for forming a catalyst material is disclosed in Patent Literature 1, in which a catalyst material containing a platinum atomic layer is produced by substituting a copper atomic layer with a platinum atomic layer in the presence of a surfactant.